1. Field of the Invention
This invention relates in general to methods and devices for fiber optic sensing of information such as the position of one object with respect to another and electronic interpretation or translation of the information. More particularly, but without limitation, it relates to such methods and devices which sense position by means of receiving images of transmitted or reflected light indicia.
2. Description of the Prior Art
In the past there have been many devices which sense or electronically determine position by means of light indicia. For example, devices which sense the pattern of light shining through slits are shown in U.S. Pat. No. 5,258,931. The devices use Charge Coupled Devices (also called CCD's) to electronically interpret the light patterns resulting from the slits to determine position. A "ruler" with slits or marks aligned in predetermined patterns which define position along the ruler is attached to a first piece of machine on which position is to be determined. A light source and a CCD are connected to a second piece of machine. The light source and the CCD are positioned adjacent the ruler and move along the pattern of slits as the first piece is moved with respect to the second. The light source produces a pattern of light indicia corresponding to the pattern of marks or slits in the ruler adjacent the CCD. The CCD electronically senses these indicia and converts them to electronic signals. In this manner the pattern of the marks or slits on the ruler adjacent the CCD are electronically communicated and can be used to determine the relative position of the first piece with respect to the second piece.
In some situations it is not possible to position a CCD or a light source in the place desired to sense position. It may also not be possible to mechanically connect or link the CCD and light source to transfer the position relationship from the sensed position to the position of the light source and CCD. Still further, in some instances weight considerations or cost considerations make it desirable to reduce the number of position sensors and/or the number of interface circuits used.
Other devices have been used in the past to convey patterns or images by means of fiber optics. Often the need for fiber optics arises because the image or pattern to be observed is located in a location or environment which is inaccessible or hostile. For example, fiber optics can be used to view objects in chemically hostile environment. In this example one end of a bundle of optical fibers is located in the hostile environment. Illumination is provided through a small percentage of fiber bundles from the safe near end and travels via those bundles to the remote end object in the hostile environment. The image reflected or transmitted is returned via the remaining bundles to a viewer disposed at the safe near end. The bundle of fibers provides an image that has a resolution as fine as the diameter of the fibers in the bundle.
Even though bundles of optical fibers have been used in the past to convey image information, they have not been used to convey parameter information such as the value of a relative position or a temperature. Generally it was thought that this type of information could be conveyed more simply by electronics. However, in some instances it is desired to convey information in an environment which might be subject to electromagnetic interference.
Another problem with sensors of the type used in the past is that they are not as fault tolerant or rugged as desired. This is especially important in the case of instrumentation on aircraft. Weight is also an important factor in such instrumentation. Electrical sensors are not completely satisfactory in any of these considerations.